1. Field of the Invention
This invention relates generally to devices for interventional therapeutic treatment or vascular surgery for treatment of defects in the vasculature, and more particularly concerns a system and method for delivering intravascular interventional devices, such as for treatment of aneurysms.
2. Description of Related Art
Vascular interventional devices such as vasoocclusive devices are typically placed within the vasculature of the human body by use of a catheter. Vascular interventional devices such as stents can be placed within an occluded vessel to facilitate blood flow through the vessel, and vasoocclusive devices are typically either placed within a blood vessel to block the flow of blood through a vessel making up that portion of the vasculature through the formation of an embolus, or are placed within an aneurysm stemming from the vessel to form such an embolus within the aneurysm. Stents can have a wide variety of configurations, but generally need to be placed and then released at a desired location within a blood vessel. Vasoocclusive devices used for these procedures can also have a wide variety of configurations, and aneurysms have been treated with external surgically placed clips, detachable vasoocclusive balloons and embolus generating vasoocclusive devices such as one or more vasoocclusive coils.
The delivery of such vasoocclusive devices have typically been accomplished by a variety of means, including via a catheter in which the device is pushed through an opening at the distal end of the catheter by a pusher to deploy the device. The vasoocclusive devices can be produced in such a way that they will pass through the lumen of a catheter in a linear shape and take on a complex shape as originally formed after being deployed into the area of interest, such as an aneurysm.
Some conventional vasoocclusive devices are operated by pulling or jerking the catheter tip from the balloon, thus potentially compromising the position of the implant. One such device provides for an endovascular wire and tip that can be separated from the holding wire mechanically or electrolytically for the formation of thrombus in blood vessels. However, such devices that release the interventional device by mechanically breaking an intermediate section between the catheter tip and balloon can potentially leave broken or jagged ends that can potentially injure the vasculature.
One conventional releasable balloon catheter used to embolize vascular lesions has a tube portion made of a material such as a hydrophilic polymer, located between the catheter and the balloon, that can be broken by torsion of the tube. The tube can be melted by heating the tube, or can be dissolved in the blood when heated, and electrodes are provided for heating the tube. Another conventional technique for separating a balloon from a balloon catheter involves the melting and breaking of a connecting member made from polyvinyl alcohol or trans-polyisoprene between the balloon and the catheter body, when power is supplied to electrodes provided for heating the connecting member. When the connecting member is heated to temperatures of about 70.degree. C. and slight tension is applied, the balloon can be separated from the main catheter body. However, such devices that release the interventional device by melting or dissolving the intermediate section between the catheter tip and balloon can also potentially release undesirable particles of materials into the bloodstream.
There is therefore a need for a precise method of deploying therapeutic interventional devices without compromising the position of the implant, without presenting broken or jagged ends that can potentially injure the vasculature, and without releasing undesirable particles of materials into the bloodstream.
The transmittal of energy of various types through a catheter to a remote location in the body has been used in the past, both for therapeutic purposes and to perform actuation or chemical reactions for delivery systems. In one such system, a temporary stent formed from a coil of tubular thermoplastic material is delivered activated for use by a heating element. The thermoplastic stent body is introduced into the vessel to be supported and is then heated by the heating element above its softening temperature and expanded to a second dimension in order to support the vessel. Cooling of the stent body allows the stent to temporarily support the vessel, and the stent body can be heated at a later time to soften and remove the stent from the vessel. However, the thermoplastic stent body contains an electrical resistance heating element, and heat is generated in the stent by a current is passed through electrically conductive wires.
An endovascular stent and delivery system is also known in which a partially cured material is delivered to a selected site in a blood vessel and is then crosslinked in the blood vessel by laser light energy delivered to the partially cured material. The delivery system can also use thermal energy as from a resistive heating element, radio frequency energy, or beta rays in order to cause the crosslinking.
A flexible guide is also known that is formed from a two-way shape memory alloy for use in non-invasive procedures. The device comprises an elongated, flexible guide having a core of a shape memory alloy which allows for tip-deflection and rotational movement to the guide wire in response to heating provided by transmission of an electrical current through the shape memory alloy.
Another catheter is known that is composed of a main body fitted with a shape memory alloy, with a liquid injector for supplying a warming liquid such as a physiological saline or transfusion solution when the shape memory alloy is to recover an original shape.
In another delivery system for an occlusive device, energy is transmitted through a catheter to a coil and a polymeric material to occlude an aneurysm. The polymeric material is solidified by light, heat or RF energy emitted from the end of a light or energy emitting device placed outside the distal end of the guiding catheter.
A common problem with such known delivery and activation systems, conveying heat by such methods as warm liquids, light, electrical energy, radio frequency energy or beta rays, is that they are typically highly inefficient or not particularly powerful, so that once a device to be delivered is placed in the desired location, there can be a delay while sufficient thermal energy is conducted to the activation site, or in the process heat energy can be radiated or otherwise lost during transmission. It would therefore be desirable to provide a thermal energy activated delivery system for vascular interventional devices that is highly efficient and immediate, and can allow the delivery of a necessary amount of thermal energy to a specific location for deployment of an interventional device.
Heat pipes are known as extremely efficient heat transfer devices, and are much more efficient than solid metal heat sinks, for example. Such heat pipes typically have a hollow interior chamber that has been evacuated, then filled with a small amount of working fluid, and sealed. When heat is applied to one end, serving as an evaporator end, the fluid vaporizes, and carries the heat in the vaporized working fluid extremely rapidly to the other end, serving as a condenser end, where the latent heat of vaporization is released as the vapor condenses back into liquid form. The working fluid is then carried back in liquid form to the evaporator end by capillary action. There is thus a need for application of a flexible heat pipe for conducting heat to a specific desired site for the purpose of deploying interventional devices such as stents and occlusive devices. The present invention meets these and other needs.